The present invention is directed to a liquid level measuring apparatus having a fixed array of spaced analog Hall-effect sensors actuated by a float which carries magnetic means, in which apparatus the variable output of the sensors provides a measurement of the position of the float and thus of the liquid level.
Digital Hall-effect sensors have been used, as disclosed in U.S. Pat. Nos. 4,361,835 and 4,589,282, for measuring liquid levels. The level accuracy in the '835 patent is directly related to the number of sensors. The '282 patent increased the accuracy of the digital sensors by the use of a complex compound magnetic float.
The present liquid level measuring apparatus and method use a plurality of spaced analog output voltage Hall-effect sensors, generally known as linear output Hall-effect sensors, in which the variable output of a sensor is a measurement of the position of the magnetic float relative to the sensor, and thus is a measurement of the liquid level. This provides a liquid level measurement with an accuracy greater than that obtained by the fixed spacing of the Hall-effect sensors. However, the voltage output of each analog Hall-effect sensor of a similar type varies due to manufacturing differences. The present invention overcomes this problem by calibrating the array of analog Hall-effect sensors relative to the position of the magnetic float, storing the calibrated values, during operation measuring the voltage outputs of any sensors activated by the presence of the magnetic float, and thereafter determining the location of the float by comparing the measured outputs with the stored values.